Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations declare it is a non-read-only (mutating) operation that is not destructive, so the safety profile is partly covered. The description adds value beyond that: the one-per-account limit, the program-active precondition, and the anti-brute-force warning are all behavioral facts not present in the structured fields.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Two tight sentences: the purpose is front-loaded and the constraints follow with zero filler. Every clause earns its place.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With an output schema present, return values need no explanation, and annotations cover the safety profile. The description covers the precondition, the once-per-account limit, and the anti-abuse rule, which is nearly complete for a one-parameter mutation, though code-format expectations remain thin.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 0% for the single "code" parameter, so the schema only conveys type and length bounds (4-20). The description implies provenance (a friend's real code) and forbids fabrication, but adds no format or syntax detail, leaving the semantics only partially supplemented.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description gives a specific verb+resource ("Apply a friend's referral code") that clearly separates it from the referral-adjacent sibling ucode_credit_referral_stats (read stats) versus this (redeem). It does not explicitly name a sibling to contrast with, so it falls just short of the top anchor.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

It supplies real preconditions: once per account, and only when the referral program is active. The final sentence ("Never guess, generate or loop over codes") tells the agent the code must come from a legitimate source, which is genuine usage guidance, though it never names an alternative tool.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.